A TEM study of the oxide scale development in Ni-Cr alloys

A study was undertaken to investigate the isothermal oxidation behaviour of Ni-Cr binary alloys with 10, 20 and 30 wt per cent Cr exposed in air for 50 h at 1,000°C. Analytical transmission electron microscopy along with light microscopy and X-ray diffraction were used to characterise the oxide scale. It was observed that the scaling behaviour exhibited by the Ni-Cr alloys changes from generally "non-protective" to "protective" as their Cr content increases from 10 to 30 wt per cent. The Ni-10Cr alloy formed a continuous network of NiO leading to scales of high thickness while Ni-30Cr exhibited only α-Cr₂Ο₃ at its surface. The Ni-20Cr alloy exhibited all three oxide phases and an intermediate scaling behaviour.